Sheet molding compound and fiber-reinforced composite material

ABSTRACT

A sheet molding compound which is a thickened material of an epoxy resin composition, including a component (A), a component (B), and a component (C), in which the component (A) is an epoxy resin staying at a liquid state at 25° C., the component (B) is an acid anhydride, the component (C) is an epoxy resin curing agent, and in the thickened material, at least some of epoxy groups of the component (A) and at least some of carboxy groups derived from the component (B) form ester.

This application is a continuation application of InternationalApplication No. PCT/JP2018/015027, filed on Apr. 10, 2018, which claimsthe benefit of priority of the prior Japanese Patent Application No.2017-079132, filed in Japan on Apr. 12, 2017, the content of which isincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a sheet molding compound and afiber-reinforced composite material.

BACKGROUND ART

Owing to its excellent mechanical characteristics and the like, a carbonfiber-reinforced composite material formed of carbon fiber and a matrixresin is widely used for airplanes, automobiles, and industrial uses. Inrecent years, as the use of the carbon fiber-reinforced compositematerial has increased, the scope of application thereof has alsowidened. A matrix resin as the carbon fiber-reinforced compositematerial needs to express high mechanical characteristics even in ahigh-temperature environment. Furthermore, a matrix resin as a moldingmaterial (sheet molding compound (hereinafter, described as SMC aswell), prepreg, or the like) used for manufacturing the carbonfiber-reinforced composite material needs to have excellent moldingproperties.

As a matrix resin of a molding material, a resin composition containinga thermosetting resin, with which carbon fiber is excellentlyimpregnated and which expresses excellent heat resistance after curing,is frequently used. As the thermosetting resin, a phenol resin, amelamine resin, a bismaleimide resin, an unsaturated polyester resin, anepoxy resin, and the like are used. Among these, the epoxy resincomposition is suitable as a matrix resin because this resin hasexcellent molding properties, expresses excellent heat resistance aftercuring, and enables a carbon fiber-reinforced composite materialprepared using the epoxy resin composition to exhibit high mechanicalcharacteristics.

The method for manufacturing a carbon fiber-reinforced compositematerial by molding a molding material includes an autoclave moldingmethod, a filament winding molding method, a resin injection moldingmethod, a vacuum resin injection molding method, a press molding method,and the like. Among these, the press molding method is in an increasingdemand because this method has high productivity and makes it easy toobtain a carbon fiber-reinforced composite material excellent in termsof design. As a molding material used in the press molding method, SMCconstituted with reinforcing short fiber and a matrix resin is beingactively used, because this material makes it possible to manufacture acarbon fiber-reinforced composite material having a complicated shapeand produces a carbon fiber-reinforced composite material optimal for astructural member.

For the matrix resin used in SMC, the following characteristics arerequired.

-   -   In order for carbon fiber to be impregnated with the matrix        resin at the time of manufacturing SMC, the matrix resin of SMC        is required to have an extremely low viscosity at the time of        manufacturing SMC.    -   In order to secure handleability of SMC at the time of press        molding, the matrix resin of SMC is required to be in a B stage        (a state where the matrix resin is thickened by semi-curing and        can be fluidized by heating) by being appropriately thickened        and to have appropriate tackiness (pressure sensitive        adhesiveness) and draping properties (flexibility).    -   In order to secure fluidity of the matrix resin at the time of        press molding, the matrix resin of SMC is required to maintain        the B stage for a long period of time (B stage stability).    -   In order to form SMC within a short period time at a high        temperature by the press molding method, the matrix resin of SMC        is required to be cured within a short period of time and have        high heat resistance after curing.    -   In order to secure mold release properties after press molding,        the matrix resin of SMC is required to have high stiffness after        curing.    -   In order to obtain a carbon fiber-reinforced composite material        having high mechanical characteristics and high heat resistance,        the matrix resin of SMC is required to be capable of expressing        high mechanical characteristics and high heat resistance after        curing.

Although the epoxy resin composition forms a cured material havingexcellent mechanical characteristics and heat resistance, it isdifficult for the epoxy resin composition to satisfy both the quickcuring properties and B stage stability.

That is, a curing agent curing the epoxy resin within a short period oftime makes the curing reaction rapidly proceed at room temperature, theB stage of the epoxy resin composition cannot be maintained for a longperiod of time. In contrast, with a curing agent that can maintain the Bstage of the epoxy resin composition for a long period of time, it isdifficult to cure the epoxy resin within a short period of time.

Therefore, as the matrix resin of SMC, generally, a thermosetting resincomposition obtained by diluting an unsaturated polyester resin or avinyl ester resin with styrene is used. However, the thermosetting resincomposition containing the unsaturated polyester resin or the vinylester resin causes serious cure shrinkage, there is a demand for thedevelopment of SMC using an epoxy resin composition that causes lesscure shrinkage.

As the epoxy resin composition used in SMC, the following compositionsare suggested.

(1) Resin composition formed of a hydroxyl group-containing epoxy resin,polyol, and a polyisocyanate compound (PTL 1).

(2) Resin composition formed of an epoxy resin, polyol, a polyisocyanatecompound, dicyandiamide, and a specific imidazole compound (PTL 2).

As epoxy resin compositions used in adhesives, the followingcompositions are suggested.

(3) Liquid adhesive formed of an epoxy resin, a curing agent activatedat a temperature of 20° C. to 100° C., and a curing agent activated at atemperature of 100° C. to 200° C. (PTL 3).

(4) Reactive hot melt adhesive containing an epoxy resin staying in asolid state at room temperature, an epoxy resin staying in a liquidstate at room temperature, amino group-terminated linearpolyoxypropylene, and a latent curing agent (dicyandiamide) (PTL 4).

As epoxy resin compositions used in prepreg, the following compositionsare suggested.

(5) Resin composition for impregnation containing an epoxy resin, alatent curing agent, a resin having a polymerizable unsaturated group,and a polymerization initiator (PTL 5).

(6) Epoxy resin composition containing an epoxy resin, an acidanhydride, and a Lewis acid salt (boron trichloride amine complex) (PTL6 to 8).

As an epoxy resin composition capable of causing an epoxy resin tostably shift to the B stage, the following composition is suggested.

(7) Resin composition containing an epoxy resin and2,5-dimethyl-2,5-hexamethylenediamine and mencenediamine as curingagents (NPL 1).

CITATION LIST Patent Literature

-   [PTL 1] Japanese Unexamined Patent Application, First Publication    No. S58-191723-   [PTL 2] Japanese Unexamined Patent Application, First Publication    No. H4-088011-   [PTL 3] Japanese Unexamined Patent Application, First Publication    No. H2-088684-   [PTL 4] Japanese Unexamined Patent Application, First Publication    No. H2-088685-   [PTL 5] Japanese Unexamined Patent Application, First Publication    No. H2-286722-   [PTL 6] Japanese Unexamined Patent Application, First Publication    No. 2004-189811-   [PTL 7] Japanese Unexamined Patent Application, First Publication    No. 2004-43769-   [PTL 8] Japanese Unexamined Patent Application, First Publication    No. 2001-354788

Non-Patent Literature

-   [NPL 1] Masaki Shimbo, “Epoxy Resin Handbook”, Nikkan Kyogyo    Shimbun, Ltd., Dec. 25, 1987, p. 155

DISCLOSURE OF INVENTION Technical Problem

The resin compositions described in (1) and (2) exploit a urethanationreaction. Accordingly, due to the influence of moisture in the resincompositions, a thickening reaction rate and the condition of the Bstage significantly change. Therefore, it is difficult to secure thehandleability and workability of SMC and the B stage stability.

The liquid adhesive described in (3) uses a curing agent (polyamine,mercaptan, isocyanate, imidazole, polyamide, polysulfide phenol, a BF₃complex, ketimine, or the like) activated at a temperature of 20° C. to100° C. Accordingly, this adhesive is gelated by a curing reaction as afirst stage. Therefore, this adhesive exhibits low fluidity beforecuring as a second stage and is not easily bulked up, and consequently,cannot be used as a matrix resin of SMC.

(4) The reactive hot melt adhesive described in (4) has high viscosity,and reinforcing fiber cannot be excellently impregnated with theadhesive. Consequently, the adhesive cannot be used as a matrix resin ofSMC.

PTL 5 describes that in a case where prepreg is manufactured using theresin composition for impregnation described in (5), a solvent isincorporated into the resin composition for impregnation, and heating isperformed such that the solvent is removed and a curing reactionpartially proceeds. With this method, a solvent is easily removed.Therefore, this method is applicable to the manufacturing of thinprepreg in which a temperature variation resulting from thickness at thetime of heating and cooling is small. However, in a thick sheet such asSMC, it is difficult to remove a solvent, and a large temperaturevariation occurs. Therefore, a defective product is obtained in whichthe surface condition becomes different from the interior conditionafter the B stage.

The epoxy resin composition described in (6) consumes a long time untilit shifts to the B stage at room temperature (23° C.). Furthermore,after the shift to the B stage at room temperature, the composition haslow viscosity and extremely strong tackiness. Therefore, thiscomposition is unsuitable for SMC.

The resin composition described in (7) contains2,5-dimethyl-2,5-hexanediamine. Therefore, the pot life of thecomposition is short. In addition, because this resin compositioncontains mecenediamine, the curing properties thereof are insufficient.Accordingly, this composition is unsuitable for a matrix resin of SMC.

The present invention provides a sheet molding compound which isexcellent in handleability (tackiness and draping properties) andfluidity and quick curing properties of a matrix resin at the time ofpressing molding, can inhibit the occurrence of burrs, and makes itpossible to obtain a fiber-reinforced composite material excellent inmold release properties, mechanical characteristics, and heatresistance; and a fiber-reinforced composite material excellent in moldrelease properties, mechanical characteristics, and heat resistance.

Solution to Problem

As a result of conducting an intensive examination, the inventors of thepresent invention have found that the above object can be achieved byusing a specific epoxy resin, an acid anhydride, and an epoxy resincuring agent, and have accomplished the present invention.

The present invention has the following aspects.

[1] A sheet molding compound which is a thickened material of an epoxyresin composition, containing: a component (A), a component (B), and acomponent (C), in which the component (A) is an epoxy resin staying in aliquid state at 25° C., the component (B) is an acid anhydride, thecomponent (C) is an epoxy resin curing agent, and in the thickenedmaterial, at least some of epoxy groups of the component (A) and atleast some of carboxy groups derived from the component (B) form ester.

[2] The sheet molding compound described in [1], further containingreinforcing fiber.

[3] The sheet molding compound described in [1] or [2], in which aviscosity of the epoxy resin composition that is measured by viscometry(a) at 30° C. 30 minutes after the preparation of the composition is 0.5to 15 Pa·s.

Viscometry (a): immediately after being prepared, the epoxy resincomposition is put and sealed into an airtightable container and left tostand for 30 minutes at 23° C., and then a viscosity of the epoxy resincomposition at 30° C. is measured.

[4] The sheet molding compound described in any one of [1] to [3], inwhich a viscosity of the epoxy resin composition that is measured byviscometry (b) at 30° C. 10 days after the preparation of thecomposition is 2,000 to 55,000 Pa·s.

Viscometry (b): immediately after being prepared, the epoxy resincomposition is put and sealed into an airtightable container and left tostand for 10 days at 23° C., and then a viscosity of the epoxy resincomposition at 30° C. is measured.

[5] The sheet molding compound described in any one of [1] to [3], inwhich a viscosity of the epoxy resin composition that is measured byviscometry (c) at 30° C. 20 days after the preparation of thecomposition is 2,000 to 100,000 Pa·s.

Viscometry (c): immediately after being prepared, the epoxy resincomposition is put and sealed into an airtightable container and left tostand for 20 days at 23° C., and then a viscosity of the epoxy resincomposition at 30° C. is measured.

[6] The sheet molding compound described in any one of [1] to [3], inwhich a viscosity of the epoxy resin composition that is measured byviscometry (b) at 30° C. 10 days after the preparation of thecomposition is 2,000 to 55,000 Pa·s, the viscosity of the epoxy resincomposition that is measured by viscometry (c) at 30° C. 20 days afterthe preparation of the composition described below is 2,000 to 100,000Pa·s, and a viscosity (b) measured by the viscometry (b) and a viscosity(c) measured by the viscometry (c) satisfy a relationship of [viscosity(c)]/[viscosity (b)]≤3.

Viscometry (b): immediately after being prepared, the epoxy resincomposition is put and sealed into an airtightable container and left tostand for 10 days at 23° C., and then a viscosity of the epoxy resincomposition at 30° C. is measured.

Viscometry (c): immediately after being prepared, the epoxy resincomposition is put and sealed into an airtightable container and left tostand for 20 days at 23° C., and then a viscosity of the epoxy resincomposition at 30° C. is measured.

[7] The sheet molding compound described in any one of [1] to [6], inwhich a content of the component (B) is such that the amount of acidanhydride groups with respect to 1 equivalent of epoxy groups containedin the epoxy resin composition becomes 0.1 to 0.5 equivalents.

[8] The sheet molding compound described in any one of [1] to [7], inwhich a content of the component (B) is 3 to 30 parts by mass withrespect to 100 parts by mass of the entire epoxy resin contained in theepoxy resin composition.

[9] The sheet molding compound described in any one of [1] to [8], inwhich a content of the component (C) is 0.1 to 25 parts by mass withrespect to 100 parts by mass of the entire epoxy resin contained in theepoxy resin composition.

[10] The sheet molding compound described in any one of [1] to [9], inwhich the component (A) contains a glycidyl amine-based epoxy resin.

[11] The sheet molding compound described in [10], in which a content ofthe glycidyl amine-based epoxy resin with respect to 100 parts by massof the entire epoxy resin contained in the epoxy resin composition is 1to 30 parts by mass.

[12] The sheet molding compound described in any one of [1] to [11], inwhich the component (B) stays in a liquid state at 25° C.

[13] The sheet molding compound described in any one of [1] to [12], inwhich the component (C) stays in a solid state at 25° C.

[14] The sheet molding compound described in any one of [1] to [13], inwhich the component (B) contains a compound having two cyclic acidanhydrides in a molecule.

[15] The sheet molding compound described in any one of [1] to [14], inwhich the component (B) contains a phthalic anhydride or a hydrogenatedphthalic anhydride that may have a substituent.

[16] The sheet molding compound described in any one of [1] to [15], inwhich the component (B) contains a hydrogenated phthalic anhydride thatmay have a substituent, and the hydrogenated phthalic anhydride that mayhave a substituent is a compound represented by Formula (1) or acompound represented by Formula (2).

[17] The sheet molding compound described in any one of [1] to [16], inwhich the component (C) contains an imidazole-based compound having amelting point of 120° C. to 300° C.

[18] The sheet molding compound described in any one of [1] to [17], inwhich the epoxy resin composition further contains a component (D), thecomponent (D) is dicyandiamide, and a content of the component (D) withrespect to 100 parts by mass of the entire epoxy resin contained in theepoxy resin composition is 0.1 to 5 parts by mass.

[19] The sheet molding compound described in any one of [1] to [18], inwhich the component (C) further contains a component (E), the component(E) is an imidazole-based compound staying in a liquid state at 25° C.,and a content of the component (E) with respect to 100 parts by mass ofthe entire epoxy resin contained in the epoxy resin composition is 0.01to 0.2 parts by mass.

A fiber-reinforced composite material which is a cured material of thesheet molding compound described in any one of [1] to [19].

[21] The sheet molding compound described in [14], in which the compoundhaving two cyclic acid anhydrides in a molecule is at least one kind ofcompound selected from the group consisting of glycerylbisanhydrotrimellitate monoacetate, ethylene glycolbisanhydrotrimellitate, pyromellitic anhydride, benzophenonetetracarboxylic anhydride, 1,2,3,4-cyclobutane tetracarboxylicdianhydride, bicyclo[2.2.2]-oct-7-ene-2,3,5,6-tetracarboxylicdianhydride, diphenyl-3,3′,4,4′-tetracarboxylic di anhydride,cyclopentane tetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride,4-(2,5-dioxotetrahydrofuran-3-yl)-tetralin-1,2-dicarboxylic anhydride,5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylicanhydride, N,N-bis[2-(2,6-dioxomorpholino)ethyl]glycine,4,4′-sulfonyldiphthalic anhydride,4,4′-ethylenebis(2,6-morpholinedione),4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride), and4,4′-(hexafluoroisopropylidene)diphthalic anhydride.

[22] The sheet molding compound described in [17], in which theimidazole-based compound having a melting point of 120° C. to 300° C. is2,4-diamino-6-[2′-methylimidazolyl-(1′)]-ethyl-s-triazine.

[23] The sheet molding compound described in [19], in which thecomponent (E) is at least one kind of compound selected from the groupconsisting of 2-ethyl-4-methylimidazole, 1,2-dimethylimidazole,1-benzyl-2-methylimidazole, and 1-benzyl-2-phenylimidazole.

[24] The sheet molding compound described in [10], in which the glycidylamine-based epoxy resin is N,N,N′,N′-tetraglycidyl-m-xylylenediamine.

Advantageous Effects of Invention

The sheet molding compound of the present invention is excellent inreinforcing fiber impregnation properties, B stage stability,handleability (tackiness and draping properties) after the shift to theB stage, storage stability, quick curing properties at the time ofheating, and fluidity and quick curing properties of a matrix resin atthe time of press molding, and less causes a burr in a die.

Furthermore the fiber-reinforced composite material of the presentinvention that is a cured material of the sheet molding compound isexcellent in mold release properties, stiffness, mechanicalcharacteristics, and heat resistance.

BEST MODE FOR CARRYING OUT THE INVENTION

The following definitions of terms are applied to the presentspecification and claims.

“Staying in a liquid state at 25° C.” means that a substance stays in aliquid state under the condition of 25° C. and 1 atm.

“Staying in a solid state at 25° C.” means that a substance stays in asolid state under the condition of 25° C. and 1 atm.

“Epoxy resin” is a compound having two or more epoxy groups in amolecule.

“Acid anhydride group” is a group having a structure formed in a casewhere one water molecule is removed from two acid groups (carboxy groupsand the like).

“Acid anhydride” is a compound having an acid anhydride group.

“Hydrogenated phthalic anhydride” is a compound formed in a case wheresome or all of unsaturated carbon bonds in a benzene ring of phthalicanhydride are substituted with a saturated carbon bond.

“Viscosity” is a value measured using a rheometer under the condition ofmeasurement mode: constant stress, stress level: 300 Pa, frequency: 1.59Hz, plate diameter: 25 mm, plate type: parallel plate, and plate gap:0.5 mm.

“Burr” is an unnecessary portion which is formed at the end of a moldedarticle by a resin flowing and solidified in voids of a die at the timeof press molding.

“To” used for describing a range of numerical values means that therange includes numerical values listed before and after “to” as a lowerlimit and an upper limit.

<<Sheet Molding Compound>>

The sheet molding compound of the present invention is a thickenedmaterial of an epoxy resin composition which will be described later.

<Epoxy Resin Composition>

The epoxy resin composition used in the present invention contains acomponent (A): epoxy resin staying in a liquid state at 25° C., acomponent (B): acid anhydride, and a component (C): epoxy resin curingagent.

Due to the action of the component (B) and the component (A), an esterbond is formed in the epoxy resin composition, and hence the compositionis thickened immediately after being prepared. The sheet moldingcompound of the present invention is the thickened material.

The epoxy resin composition may further contain a component (D):dicyandiamide. In the epoxy resin composition of the present invention,the component (C) may further contain a component (E): imidazole-basedcompound staying in a liquid state at 25° C. As long as the effects ofthe present invention are not impaired, if necessary, the epoxy resincomposition used in the present invention may contain other components.

The viscosity of the epoxy resin composition that is measured by thefollowing viscometry (a) at 30° C. 30 minutes after the preparation ofthe composition is preferably 0.5 to 15 Pa·s, more preferably 0.5 to 10Pa·s, and even more preferably 1 to 5 Pa·s. In a case where theviscosity measured at 30° C. 30 minutes after the preparation of thecomposition is equal to or higher than 0.5 Pa·s and more preferablyequal to or higher than 1 Pa·s, at the time of manufacturing the sheetmolding compound of the present invention, the accuracy of a basisweight (thickness of the epoxy resin composition) at the time of coatinga film with the epoxy resin composition tends to be easily stabilized.Furthermore, in a case where the viscosity measured at 30° C. 30 minutesafter the preparation of the composition is equal to or lower than 15Pa·s, more preferably equal to or lower than 10 Pa·s, and even morepreferably equal to or lower than 5 Pa·s, at the time of manufacturingthe sheet molding compound by using the epoxy resin composition,reinforcing fiber, and the like, the reinforcing fiber tends to beimpregnated better with the epoxy resin composition.

Viscometry (a): immediately after being prepared, the epoxy resincomposition is put and sealed into an airtightable container and left tostand for 30 minutes at 23° C., and then a viscosity of the epoxy resincomposition at 30° C. is measured.

The viscosity of the epoxy resin composition measured by the followingviscometry (b) at 30° C. 10 days after the preparation of thecomposition is preferably 2,000 to 55,000 Pa·s, more preferably 2,000 to42,000 Pa·s, and even more preferably 4,000 to 20,000 Pa·s. In a casewhere the viscosity measured at 30° C. 10 days after the preparation ofthe composition is equal to or higher than 2,000 Pa·s, and morepreferably equal to or higher than 4,000 Pa·s, at the time of handlingthe sheet molding compound, the surface tackiness tends to be reduced.In a case where the viscosity measured at 30° C. 10 days after thepreparation of the composition is equal to or lower than 55,000 Pa·s,more preferably equal to or lower than 42,000 Pa·s, and even morepreferably equal to or lower than 20,000 Pas, the draping properties ofthe sheet molding compound fall into an appropriate range, and thehandleability tend to become excellent.

Viscometry (b): immediately after being prepared, the epoxy resincomposition is put and sealed into an airtightable container and left tostand for 10 days at 23° C., and then a viscosity of the epoxy resincomposition at 30° C. is measured.

The viscosity of the epoxy resin composition measured by the followingviscometry (c) at 30° C. 20 days after the preparation of thecomposition is preferably 2,000 to 100,000 Pa·s, more preferably 4,000to 80,000 Pa·s, and even more preferably 5,000 to 70,000 Pa·s. In a casewhere the viscosity measured at 30° C. 20 days after the preparation ofthe composition is equal to or higher than 2,000 Pa·s, more preferablyequal to or higher than 4,000 Pa·s, and even more preferably equal to orhigher than 5,000 Pa·s, at the time of handling the sheet moldingcompound, the surface tackiness tends to be reduced. In a case where theviscosity measured at 30° C. 20 days after the preparation of thecomposition is equal to or lower than 100,000 Pa·s, more preferablyequal to or lower than 80,000 Pa·s, and even more preferably equal to orlower than 70,000 Pa·s, the draping properties of the sheet moldingcompound fall into an appropriate range, and the handleability tends tobecome excellent.

In a case where the viscosity measured at 30° C. 20 days after thepreparation of the composition is within the above range, it isunderstood that the composition is capable of maintaining the B stagefor a long period of time (B stage stability is excellent).

It is preferable that a viscosity (b) measured by the viscometry (b) anda viscosity (c) measured by the viscometry (c) satisfy a relationship of[viscosity (c)]/[viscosity (b)]≤3, because then the B stage stabilitytends to be further improved, the viscosity of the sheet moldingcompound tends to change less over time, and the storage stability tendsto become excellent. [Viscosity (c)]/[viscosity (b)] is more preferablywithin a range of 0.3 to 3, and even more preferably within a range of0.5 to 3.

(Component (A))

The component (A) is an epoxy resin staying in a liquid state at 25° C.

The component (A) is a component which adjusts the viscosity of theepoxy resin composition to be within the above range such thatreinforcing fiber is impregnated better with the epoxy resin compositionat the time of manufacturing the sheet molding compound. Furthermore,the component (A) is a component which improves the mechanicalcharacteristics and heat resistance of a fiber-reinforced compositematerial which is a cured material of the sheet molding compound. In acase where the component (A) has an aromatic ring, it is easy to adjustthe mechanical characteristics of the fiber-reinforced compositematerial to be within a desired range.

Examples of the component (A) include glycidyl ether of bisphenols(bisphenol A, bisphenol F, bisphenol AD, halogen-substituted bisphenolsA, F, and AD, and the like); glycidyl ether of polyphenols obtained by acondensation reaction between phenols and an aromatic carbonyl compound;glycidyl ether of polyols (polyoxyalkylene bisphenol A and the like); apolyglycidyl compound derived from aromatic amines; and the like.

As the component (A), a bisphenol-type epoxy resin is preferable,because this resin makes it easy to adjust the viscosity of the epoxyresin composition to be appropriate for impregnating reinforcing fiberwith the composition, and makes it easy to adjust the mechanicalcharacteristics of the fiber-reinforced composite material to be withina desired range.

As the bisphenol-type epoxy resin, a difunctional bisphenol-type epoxyresin is preferable. A bisphenol A-type epoxy resin is more preferable,because the heat resistance and the chemical resistance of thefiber-reinforced composite material become excellent. A bisphenol F-typeepoxy resin is more preferable, because the viscosity of this resin islower than that of the bisphenol A-type epoxy resin having theapproximately same molecular weight, and the elastic modulus of thefiber-reinforced composite material becomes high.

Herein, “difunctioinal bisphenol-type epoxy resin” means abisphenol-type epoxy resin having two epoxy groups in a molecule.

The component (A) may be an epoxy resin having three or more functionalgroups. A trifunctional epoxy resin and a tetrafunctional epoxy resincan further improve the heat resistance of the fiber-reinforcedcomposite material without significantly change the viscosity of theepoxy resin composition.

Herein, “trifunctional epoxy resin” means a resin having three epoxygroups in a molecule. “Tetrafunctional epoxy resin” means a resin havingfour epoxy groups in a molecule.

Examples of commercial products of the difunctional bisphenol-type epoxyresin include the following ones.

jER (registered trademark) 825, 827, 828, 828EL, 828XA, 806, 806H, 807,4004P, 4005P, 4007P, and 4010P manufactured by Mitsubishi ChemicalCorporation,

EPICLON (registered trademark) 840, 840-S, 850, 850-S, EXA-850CRP,850-LC, 830, 830-S, 835, EXA-830CRP, EXA-830LVP, and EXA-835LVmanufactured by DIC Corporation,

EPOTORT (registered trademark) YD-115, YD-115G, YD-115CA, YD-118T,YD-127, YD-128, YD-128G, YD-128S, YD-128CA, YDF-170, YDF-2001, YDF-2004,and YDF-2005RL manufactured by NIPPON STEEL & SUMIKIN CHEMICAL CO.,LTD., and the like.

Examples of commercial products of the component (A) having two or morefunctional groups include the following ones.

jER (registered trademark) 152, 154, 157S70, 1031S, 1032H60, 604, 630,and 630LSD manufactured by Mitsubishi Chemical Corporation,

N-730A, N-740, N-770, N-775, N-740-80M, N-770-70M, N-865, N-865-80M,N-660, N-665, N-670, N-673, N-680, N-690, N-695, N-665-EXP, N-672-EXP,N-655-EXP-S, N-662-EXP-S, N-665-EXP-S, N-670-EXP-S, N-685-EXP-S, andHP-5000 manufactured by DIC Corporation,

TETRAD-X manufactured by Mitsubishi Chemical Corporation, and the like.

Particularly, in a case where the component (A) contains a glycidylamine-based epoxy resin such as TETRAD-X, it is possible to hasten thetemporal change of viscosity of the epoxy resin composition. That is, ina case where the content of the glycidyl amine-based epoxy resin isadjusted, the viscosity (b) or the viscosity (c) can be controlled, theshift to the B stage proceeds within a short period of time at the timeof manufacturing the sheet molding compound, and accordingly, theproductivity thereof can be increased.

In a case where the glycidyl amine-based epoxy resin is used, thecontent of the resin is preferably about 1% to 30% by mass with respectto 100% by mass of the component (A). The content of the glycidylamine-based epoxy resin is more preferably 2% to 20% by mass, and evenmore preferably 3% to 15% by mass. In a case where the content of theglycidyl amine-based epoxy resin is equal to or greater than 1% by mass,more preferably equal to or greater than 2% by mass, and even morepreferably equal to or greater than 3% by mass, the time taken for thesheet molding compound to shift to the B stage tends to be suitablyreduced. Furthermore, in a case where the content of the glycidylamine-based epoxy resin is equal to or smaller than 30% by mass, morepreferably equal to or smaller than 20% by mass, and even morepreferably equal to or smaller than 15% by mass, the storage stabilityof the sheet molding compound tends to be improved.

One kind of component (A) may be used singly, or two or more kinds ofcomponents (A) may be used in combination.

The content of the component (A) in the epoxy resin composition used inthe present invention may be set such that the viscosity of the epoxyresin composition measured at 30° C. 30 minutes after the preparation ofthe composition becomes 0.5 to 15 Pa·s. The content of the component (A)varies with the type of the component (A).

The content of the component (A) with respect to 100 parts by mass ofthe entire epoxy resin contained in the epoxy resin composition ispreferably 20% to 100% by mass, and more preferably 50% to 95% by mass.In a case where the content of the component (A) is within the aboverange, it is easy to adjust the viscosity of the epoxy resin compositionto be within the above range, and the reinforcing fiber impregnationproperties are improved. Furthermore, the heat resistance of thefiber-reinforced composite material is improved.

(Component (B))

The component (B) is an acid anhydride.

The component (B) is a component which can act on the component (A) atroom temperature and thickens the epoxy resin composition immediatelyafter the composition is prepared such that the sheet molding compoundshifts to the B stage.

It is preferable that the component (B) stays in a liquid state at 25°C. In a case where the component (B) has the above properties, thecomponents in the epoxy resin composition can be uniformly mixedtogether, and the epoxy resin composition can be uniformly thickened.

Examples of the component (B) include a cyclic acid anhydride having astructure formed in a case where one or more water molecules are removedfrom two or more acids in a molecule. The cyclic acid anhydride includesa compound having one cyclic acid anhydride group or two or more cyclicacid anhydride groups in a molecule.

Examples of the compound having one cyclic acid anhydride group includedodecenyl succinic anhydride, polyadipic anhydride, polyazelaicanhydride, methyl tetrahydrophthalic anhydride, methyl hexahydrophthalicanhydride, methyl himic anhydride, hexahydrophthalic anhydride, phthalicanhydride, trimellitic anhydride, 3-acetamidophthalic anhydride,4-pentene-1,2-dicarboxylic anhydride,6-bromo-1,2-dihydro-4H-3,1-benzoxazine-2,4-dione, 2,3-anthracenedicarboxylic anhydride, and the like.

Examples of the compound having two cyclic acid anhydride groups includeglyceryl bisanhydrotrimellitate monoacetate, ethylene glycolbisanhydrotrimellitate, pyromellitic anhydride, benzophenonetetracarboxylic anhydride, 1,2,3,4-cyclobutane tetracarboxylicdianhydride, bicyclo[2.2.2]-oct-7-ene-2,3,5,6-tetracarboxylicdianhydride, diphenyl-3,3′,4,4′-tetracarboxylic dianhydride,cyclopentane tetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride,4-(2,5-dioxotetrahydrofuran-3-yl)-tetralin-1,2-dicarboxylic anhydride,5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylicanhydride, N,N-bis[2-(2,6-dioxomorpholino)ethyl]glycine,4,4′-sulfonyldiphthalic anhydride,4,4′-ethylenebis(2,6-morpholinedione),4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride),4,4′-(hexafluoroisopropylidene)diphthalic anhydride, and the like.

As the component (B), in view of the stability of viscosity of the epoxyresin composition and the heat resistance or mechanical characteristicsof the cured material of the epoxy resin composition, phthalic anhydrideor hydrogenated phthalic anhydride which may have a substituent ispreferable, and a compound represented by Formula (I) or a compoundrepresented by Formula (2) is more preferable.

As the component (B), it is preferable to use a compound having twocyclic acid anhydrides in a molecule, because then the occurrence ofburrs at the time of press molding can be reduced.

One kind of component (B) may be used singly, or two or more kinds ofcomponents (B) may be used in combination.

The content of the component (B) is preferably set such that the amountof acid anhydride groups with respect to 1 equivalent of epoxy groupscontained in the epoxy resin composition becomes 0.1 to 0.5 equivalents,more preferably set such that the amount of the acid anhydride groupsbecomes 0.1 to 0.4 equivalents, and even more preferably set such thatthe amount of the acid anhydride groups becomes 0.1 to 0.3 equivalents.In a case where the content of the component (B) is within the aboverange, the sheet molding compound appropriately shifts to the B stage.In a case where the content of the component (B) is equal to or greaterthan the lower limit of the above range, the sheet molding compoundtends to excellently shift to the B stage, appropriate tackiness tendsto be obtained, and the mold release properties of a carrier film fromthe sheet molding compound tends to become excellent. In a case wherethe content of the component (B) is equal to or smaller than the upperlimit of the above range, the sheet molding compound tends toappropriately shift to the B stage, excellent draping properties tend tobe obtained, and the workability of cutting, lamination, and the like ofthe sheet molding compound tends to become excellent.

The content of the component (B) with respect to 100 parts by mass ofthe entire epoxy resin contained in the epoxy resin composition ispreferably 3 to 30 parts by mass. The content of the component (B) ismore preferably 5 to 25 parts by mass, and even more preferably 8 to 20parts by mass. In a case where the content of the component (B) iswithin the above range, the sheet molding compound appropriately shiftsto the B stage. In a case where the content of the component (B) withrespect to 100 parts by mass of the entire epoxy resin contained in theepoxy resin composition is equal to or greater than 3 parts by mass,more preferably equal to or greater than 5 parts by mass, and even morepreferably equal to or greater than 8 parts by mass, the sheet moldingcompound tends to excellently shift to the B stage, appropriatetackiness tends to be obtained, and the release properties of a carrierfilm from the sheet molding compound tend to become excellent. In a casewhere the content of the component (B) with respect to 100 parts by massof the entire epoxy resin contained in the epoxy resin composition isequal to or smaller than 30 parts by mass, more preferably equal to orsmaller than 25 parts by mass, and even more preferably equal to orsmaller than 20 parts by mass, the sheet molding compound tends toappropriately shift to the B stage, excellent draping properties tend tobe obtained, and the workability of cutting, lamination, and the like ofthe sheet molding compound tends to become excellent.

In a case where the aforementioned compound having two cyclic acidanhydrides in a molecule is used as the component (B), the content ofthe compound with respect to 100 parts by mass of the entire epoxy resincontained in the epoxy resin composition is preferably 1 to 20 parts bymass. The content of the compound is more preferably 1 to 10 parts bymass, and even more preferably 1 to 5 parts by mass.

In a case where the content of the compound having two cyclic acidanhydrides in a molecule is equal to or greater than 1 parts by masswith respect to 100 parts by mass of the entire epoxy resin contained inthe epoxy resin composition, the occurrence of burrs at the time ofpress-molding the sheet molding compound tends to be reduced.Furthermore, in a case where the content of the compound having twocyclic acid anhydrides in a molecule with respect to 100 parts by massof the entire epoxy resin contained in the epoxy resin composition isequal to or smaller than 20% by mass, more preferably equal to orsmaller than 10 parts by mass, and even more preferably equal to orsmaller than 5 parts by mass, the fluidity of the sheet molding compoundin a molding die at the time of press molding tends to become excellent.

(Component (C))

The component (C) is an epoxy resin curing agent.

The component (C) is a component which functions as a curing agent forthe epoxy resin and acts as a catalyst so as to cause the component (A)and the component (B) to react with each other at room temperature atthe time of shift to the B stage during which the component (A) and thecomponent (B) react with each other.

It is preferable that the component (C) stays in a solid state at 25° C.In a case where the component (C) has the above properties, the reactionof the component (C) tends to be inhibited at the time of manufacturingthe sheet molding compound or at the time of storing the manufacturedsheet molding compound, and the productivity, storage stability,handleability, fluidity at the time of molding, and the like of thesheet molding compound tend to become excellent.

Examples of the component (C) include aliphatic amine, aromatic amine,modified amine, secondary amine, tertiary amine, an imidazole-basedcompound, mercaptans, and the like.

As the component (C), in view of the storage stability of the sheetmolding compound containing the epoxy resin composition described above,an imidazole-based compound having a melting point of 120° C. to 300° C.is preferable. For example,2,4-diamino-6-[2′-methylimidazolyl-(1′)]-ethyl-s-triazine can besuitably used.

In a case where an imidazole-based compound staying in a liquid state at25° C. (hereinafter, referred to as component (E) as well) is used asthe component (C), it is possible to reduce the time taken for the sheetmolding compound to shift to the B stage.

Examples of the component (E) include 2-ethyl-4-methylimidazole,1,2-dimethylimidazole, 1-benzyl-2-methylimidazole,1-benzyl-2-phenylimidazole, and the like.

The content of the component (E) with respect to 100 parts by mass ofthe entire epoxy resin contained in the epoxy resin composition ispreferably 0.01 to 0.2 parts by mass, more preferably 0.01 to 0.1 partsby mass, and even more preferably 0.03 to 0.07 parts by mass. In a casewhere the content is equal to or greater than 0.01 parts by mass, andpreferably equal to or greater than 0.03 parts by mass, the time takenfor the sheet molding compound to shift to the B stage tends to bereduced. Furthermore, in a case where the content is equal to or smallerthan 0.2 parts by mass, more preferably equal to or smaller than 0.1part by mass, and even more preferably equal to or smaller than 0.07parts by mass, the stability of the shift to the B stage of the sheetmolding compound tends to become excellent.

One kind of component (C) may be used singly, or two or more kinds ofcomponents (C) may be used in combination.

The content of the component (C) with respect to 100 parts by mass ofthe entire epoxy resin contained in the epoxy resin composition ispreferably 0.1 to 25 parts by mass, more preferably 2 to 10 parts bymass, and even more preferably 3 to 7 parts by mass. In a case where thecontent of the component (C) is equal to or greater than 0.1 parts bymass, more preferably equal to or greater than 2 parts by mass, and evenmore preferably equal to or greater than 3 parts by mass, the quickcuring properties at the time of molding the sheet molding compoundtends to become excellent. Furthermore, in a case where the content ofthe component (C) is equal to or smaller than 25 parts by mass, morepreferably equal to or smaller than 10 parts by mass, and even morepreferably equal to or smaller than 7 parts by mass, the stability ofthe B stage at the time of manufacturing the sheet molding compoundtends to become excellent.

In some cases, the particle diameter of the component (C) at 25° C.affects the characteristics of the sheet molding compound. For example,in a case where the particle diameter of the component (C) is large, thesurface area of the component (C) becomes small, and in order to curethe epoxy resin composition within a short period of time, sometimes thecontent of the component (C) needs to be increased. In a case where theparticle diameter of the component (C) is large, the proportion of theepoxy resin composition that enters the interior of reinforcing fiber isreduced, and consequently, sometimes the time taken for curing isincreased. The average particle diameter of the component (C) ispreferably equal to or smaller than 25 μm, and more preferably equal toor smaller than 15 μm. More specifically, the average particle diameterof the component (C) is preferably larger than 0 μm and equal to orsmaller than 25 μm, and more preferably 1 to 15 μm.

The average particle diameter can be measured using a particle sizedistribution analyzer adopting an image analysis method, a laserdiffraction scattering method, a Coulter method, a centrifugalprecipitation method, or the like as measurement principle.

(Component (D))

The component (D) is dicyandiamide.

In a case where the epoxy resin composition described above furthercontains dicyandiamide, it is possible to further improve the toughnessand heat resistance of the cured material of the sheet molding compoundobtained from the epoxy resin composition without impairing the shift tothe B stage of the sheet molding compound and the stability thereof aswell as the quick curing properties.

The content of the component (D) with respect to 100 parts by mass ofthe entire epoxy resin contained in the epoxy resin composition ispreferably 0.1 to 5 parts by mass, more preferably 0.3 to 5 parts bymass, and even more preferably 1 to 4 parts by mass. In a case where thecontent of the component (D) is equal to or greater than 0.1 parts bymass, more preferably equal to or greater than 0.3 parts by mass, andeven more preferably equal to or greater than 1 part by mass, thetoughness or heat resistance of the cured material of the sheet moldingcompound tends to become excellent. Furthermore, in a case where thecontent of the component (D) is equal to or smaller than 5 parts by massand more preferably equal to or smaller than 4 parts by mass, the Bstage stability at the time of manufacturing the sheet molding compoundtends to become excellent.

(Other Components)

Examples of other components that the aforementioned epoxy resincomposition may contain if necessary include a curing accelerator for anepoxy resin, an inorganic filler, an internal release agent, asurfactant, an organic pigment, an inorganic pigment, an epoxy resincomposition other than the component (A), other resins (a thermoplasticresin, a thermoplastic elastomer, and an elastomer), and the like.

As the curing accelerator, a urea compound is preferable because thiscompound improves the mechanical characteristics (bending strength andflexural modulus) of the fiber-reinforced composite material.

Examples of the urea compound include 3-phenyl-1,1-dimethylurea,3-(3,4-dichlorophenyl)-1,1-dimethylurea,3-(3-chloro-4-methylphenyl)-1,1-dimethylurea,2,4-bis(3,3-dimethylureide)toluene,1,1′-(4-methyl-1,3-phenylene)bis(3,3-dimethylurea), and the like.

Examples of the inorganic filler include calcium carbonate, aluminumhydroxide, clay, barium sulfate, magnesium oxide, glass powder, hollowglass beads, aerosil, and the like.

Examples of the internal release agent include carnauba wax, zincstearate, calcium stearate, and the like.

In a case where the epoxy resin composition contains a surfactant, therelease properties of a carrier film from the sheet molding compound canbe improved. Furthermore, voids included in the sheet molding compoundcan be reduced.

Examples of the epoxy resin other than the component (A) include anepoxy resin which stays in a semi-solid state or solid state at 25° C.As the epoxy resin other than the component (A), an epoxy resin havingan aromatic ring is preferable, and a difunctional epoxy resin is morepreferable. Furthermore, in addition to the difunctional epoxy resin,for the purpose of improving the heat resistance of the cured materialor controlling the viscosity of the epoxy resin composition, variousepoxy resins may be incorporated into the epoxy resin composition of thepresent invention. For improving the heat resistance, a polyfunctionalepoxy resin, a novolac-type epoxy resin, or an epoxy resin having anaphthalene skeleton is effective.

By changing the viscoelasticity of the epoxy resin composition, thethermoplastic resin, the thermoplastic elastomer, and the elastomer makethe epoxy resin composition have appropriate viscosity, appropriatestorage modulus, and appropriate thixotropic properties and improve thetoughness of the cured material of the epoxy resin composition. One kindof each of the thermoplastic elastomer, the thermoplastic elastomer, andthe elastomer may be used singly, or two or more kinds of these may beused in combination.

(Method for Preparing Epoxy Resin Composition)

The epoxy resin composition of the present invention can be prepared bythe method known in the related art. For example, the epoxy resincomposition may be prepared by mixing together the components at thesame time. Alternatively, by appropriately dispersing the component (B),the component (C), and the like separately in the component (A) inadvance, a master batch may be prepared, and the epoxy resin compositionmay be prepared using the master batch. Furthermore, in a case where theinternal temperature of the system is increased due to the shear heatingcaused by kneading and the like, it is preferable to implement a methodfor inhibiting the increase of temperature, such as controlling thekneading speed or cooling the preparation kiln or the kneading kiln.Examples of kneading devices include an electric mortar, attritor, aplanetary mixer, a dissolver, a triple roll, a kneader, an all-purposestirrer, a homogenizer, a homodispenser, a ball mill, a beads mill, andthe like. Two or more kinds of kneading devices may be used incombination.

(Operation and Effect)

The epoxy resin composition used in the present invention describedabove contains the component (A): epoxy resin staying in a liquid stateat 25° C. as a main component, and accordingly, the viscosity of thejust prepared composition can be reduced. For example, after 30 minutes,the viscosity of the epoxy resin composition at 30° C. can be equal toor lower than 15 Pa·s. Therefore, reinforcing fiber can be excellentlyimpregnated with the epoxy resin composition, and the epoxy resincomposition can be suitably used for manufacturing the sheet moldingcompound.

Furthermore, the epoxy resin composition can be thickened within a shortperiod of time after being prepared. For example, the viscosity of theepoxy resin composition measured at 30° C. 10 days after the preparationof the composition can be 2,000 to 55,000 Pa·s. Therefore, the surfacetackiness can be reduced at the time of handling the sheet moldingcompound, and appropriate draping properties can be obtained.Accordingly, excellent handleability can be obtained.

In addition, the viscosity of the thickened epoxy resin composition canbe maintained for a long period of time. For example, the viscosity ofthe epoxy resin composition measured at 30° C. 20 days after thepreparation of the composition can be 2,000 to 100,000 Pa·s. Therefore,the tackiness and draping properties after the shift to the B stage andthe B stage stability become excellent.

Moreover, because the epoxy resin composition contains the component(A), the stiffness, mechanical characteristics, and heat resistance ofthe cured material of the sheet molding compound are excellent.

(Reinforcing Fiber)

The sheet molding compound may contain reinforcing fiber. As thereinforcing fiber, various fibers can be adopted according to the use orusage purpose of the sheet molding compound. Examples thereof includecarbon fiber (including graphite fiber, the same is true for thefollowing description), aramid fiber, silicon carbide fiber, aluminafiber, boron fiber, tungsten carbide fiber, glass fiber, and the like.In view of mechanical characteristics of the fiber-reinforced compositematerial, carbon fiber and glass fiber are preferable, and carbon fiberis particularly preferable.

Usually, the reinforcing fiber is used in the form of a reinforcingfiber tow constituted with 1,000 to 60,000 filaments. In a moldingmaterial, the reinforcing fiber is present by maintaining the form ofthe reinforcing fiber tow, or present by being further divided into towsconstituted with fewer filaments. Usually, in SMC, the reinforcing fiberis present by being further divided into smaller tows.

As the reinforcing fiber in SMC, chopped reinforcing fiber towsconstituted with short fiber are preferable. The length of the shortfiber is preferably 0.3 to 10 cm, and more preferably 1 to 5 cm. In acase where the length of the short fiber is equal to or greater than 0.3cm, a fiber-reinforced composite material having excellent mechanicalcharacteristics is obtained. In a case where the length of the shortfiber is equal to or smaller than 10 cm, SMC exhibiting excellentfluidity at the time of press molding is obtained.

It is more preferable that the reinforcing fiber in SMC is in the formof a sheet constituted with chopped reinforcing fiber tows that aretwo-dimensionally and randomly stacked.

(Method for Manufacturing SMC)

For example, SMC is manufactured by sufficiently impregnating asheet-like substance formed of the chopped reinforcing fiber tows withthe epoxy resin composition and thickening the epoxy resin composition.

In a case where reinforcing fiber is impregnated with the epoxy resincomposition by a known method appropriate for the form of thereinforcing fiber and then held as it is for several days to tens ofdays at a temperature of about room temperature to 60° C. or for severalseconds to tens of minutes at a temperature of about 60° C. to 80° C.,an epoxy group, which is contained in the component (A) in the epoxyresin composition and other epoxy resins optionally mixed in, and acarboxy group derived from the component (B) cause a esterificationreaction, and accordingly, the epoxy resin composition shifts to the Bstage.

It is preferable to select the reaction condition for the epoxy groupcontained in the epoxy resin and the carboxy group derived from thecomponent (B) such that the viscosity of the thickened material of theepoxy resin composition obtained after the esterification reaction thatis measured at 30° C. falls into the range described above.

As the method for impregnating the sheet-like substance of the choppedreinforcing fiber tow with the epoxy resin composition, various methodsknown in the related art can be adopted. For example, the followingmethod can be adopted.

Two sheets of films uniformly coated with the epoxy resin compositionare prepared. Chopped reinforcing fiber tows are randomly scattered onthe surface of one of the films coated with the epoxy resin composition,thereby obtaining a sheet-like substance. The surface of the other filmcoated with the epoxy resin composition is bonded to the surface of thesheet-like substance, and the sheet-like substance is pressed so as tobe impregnated with the epoxy resin composition. Then, the epoxy resincomposition is allowed to be thickened. In this way, SMC with suppressedsurface tackiness that is suitable for a molding operation is obtained.

(Operation and Effect)

SMC of the present invention described above contains the thickenedmaterial of the epoxy resin composition exhibiting excellent tackinessand draping properties after the shift to the B stage. Therefore, theSMC has excellent handleability (tackiness and draping properties).

Furthermore, SMC of the present invention contains the thickenedmaterial of the epoxy resin composition of the present invention that isexcellent in the B stage stability. Therefore, the SMC is excellent inthe fluidity of the matrix resin at the time of press molding and caninhibit the occurrence of burrs in a die.

In addition, SMC of the present invention exhibits excellent quickcuring properties at the time of press molding. Due to the high curingspeed at the time of press molding, the SMC stays in a die for a shortperiod of time, and hence the productivity of the fiber-reinforcedcomposite material is improved.

Moreover, SMC of the present invention contains the thickened materialof the epoxy resin composition producing a cured material excellent instiffness, mechanical characteristics, and heat resistance. Therefore,from the SMC, it is possible to obtain a fiber-reinforced compositematerial excellent in mold release properties, mechanicalcharacteristics, and heat resistance.

<Fiber-Reinforced Composite Material>

The fiber-reinforced composite material of the present invention is acured material of SMC of the present invention.

The fiber-reinforced composite material of the present invention ismanufactured by heat-molding SMC and curing the epoxy resin compositionhaving shifted to the B stage.

Examples of the method for manufacturing the fiber-reinforced compositematerial by using SMC include the following method.

One sheet of SMC or a substance constituted with a plurality of sheetsof stacked SMC is set between a pair of dies. SMC is heated andcompressed for 2 to 60 minutes at a temperature of 120° C. to 230° C.such that the epoxy resin composition is cured, thereby obtaining afiber-reinforced composite material as a molded article. As a corematerial, a honeycomb structure such as a corrugated board may be used,and SMC may be disposed on either or both of the surfaces thereof.

(Operation and Effect)

The fiber-reinforced composite material of the present inventiondescribed above is a cured material of SMC of the present invention.Therefore, the material is excellent in mold release properties,mechanical characteristics, and heat resistance.

Other Embodiments

The present invention is not limited to the embodiments described above,and can be modified in various ways within the scope of claims. Theembodiments, which are obtained by appropriately combining technicalmeans described in the above embodiments with other embodiments, arealso included in the technical scope of the present invention.

EXAMPLES

Hereinafter, the present invention will be more specifically describedbased on examples, but the present invention is not limited thereto.

<Components>

(Component (A))

jER (registered trademark) 828: bisphenol A-type liquid epoxy resin(manufactured by Mitsubishi Chemical Corporation, viscosity at 25° C.:12 Pa·s)

jER (registered trademark) 807: bisphenol F-type liquid epoxy resin(manufactured by Mitsubishi Chemical Corporation, viscosity at 25° C.: 4Pa·s)

jER (registered trademark) 604: tetraglycidyldiamine diphenylmethane(manufactured by Mitsubishi Chemical Corporation, viscosity at 25° C.:360 Pa·s)

jER (registered trademark) 630: triglycidyl-p-aminophenol (manufacturedby Mitsubishi Chemical Corporation, viscosity at 25° C.: 0.7 Pa·s)

TETRAD-X: N,N,N′,N′-tetraglycidyl-m-xylylenediamine (manufactured byMitsubishi Chemical Corporation, viscosity at 25° C.: 2 Pa·s)

(Component (B))

HN-2200: 3-methyl-1,2,3,6-tetrahydrophthalic anhydride or4-methyl-1,2,3,6-tetrahydrophthalic anhydride (manufactured by HitachiChemical Co., Ltd., viscosity at 25° C.: 75 mPa·s)

HN-2000: 3-methyl-1,2,3,6-tetrahydrophthalic anhydride or4-methyl-1,2,3,6-tetrahydrophthalic anhydride (manufactured by HitachiChemical Co., Ltd., viscosity at 25° C.: 40 mPa·s)

HN-5500: 3-methyl-hexahydrophthalic anhydride or4-methyl-hexahydrophthalic anhydride (manufactured by Hitachi ChemicalCo., Ltd., viscosity at 25° C.: 75 mPa·s)

MHAC-P: methyl-5-norbornene-2,3-dicarboxylic anhydride (manufactured byHitachi Chemical Co., Ltd., viscosity at 25° C.: 225 mPa·s)

HN-2200: 3-methyl-1,2,3,6-tetrahydrophthalic anhydride or4-methyl-1,2,3,6-tetrahydrophthalic anhydride (manufactured by HitachiChemical Co., Ltd.)

MH-700: mixture of 4-methyl-hexahydrophthalic anhydride andhexahydrophthalic anhydride (manufactured by New Japan Chemical Co.,Ltd.)

TMEG-600: ethylene glycol bis(anhydrotrimellitate) (manufactured by NewJapan Chemical Co., Ltd.)

MTA-15: mixture of 4-methyl-hexahydrophthalic anhydride,hexahydrophthalic anhydride, andglycerylbis(anhydrotrimellitate)monoacetate (manufactured by New JapanChemical Co., Ltd.)

(Component (C))

2MZA-PW: 2,4-diamino-6-[2′-methylimidazole-(1′)]-ethyl-s-triazine(manufactured by SHIKOKU CHEMICALS CORPORATION, inciting point: 253° C.)

(Component (D))

DICYANEX 1400F: dicyandiamide (manufactured by Air Products andChemicals, Inc.)

(Component (E))

2E4MZ: 2-ethyl-4-methylimidazole (manufactured by SHIKOKU CHEMICALSCORPORATION, melting point: 40° C.)

(Other Components)

Omicure (registered trademark) 24: 2,4-di(N,N-dimethylureide)toluene(manufactured by PTI Japan, Ltd.)

DY9577: boron trichloride amine complex (manufactured by HuntsmanCorporation, melting point: 28° C. to 35° C.)

(Preparation of Master Batch)

Each of DICYANEX 1400F, 2MZA-PW, and TMEG-600 was mixed with jER(registered trademark) 828 at 1:1 (mass ratio). The mixtures werekneaded using a triple roll, thereby obtaining a master batch.

<Preparation of Epoxy Resin Composition>

Examples 1 to 23 and Comparative Examples 1 to 3

According to the formulation shown in Table 1 to Table 5, componentswere weighed and put into a flask. For DICYANEX 1400F, 2MZA-PW, RIKACIDTH, and RIKACID TMEG-600, a master batch was used. The componentsweighed and put into the flask were uniformly stirred with a stirrer atroom temperature, thereby obtaining an epoxy resin composition. Thefollowing measurement and evaluation were performed. The results areshown in Table 1 to Table 5.

(Measurement of Isothermal Viscosity)

Immediately after being prepared, the epoxy resin composition was putand sealed into an airtightable container, and stored by being left tostand in a room at 23° C. in a place protected from direct sunlight.Thirty minutes, 10 days, and 20 days after the preparation of the epoxyresin composition, the viscosity of the composition was measured asbelow.

The plate of a rheometer (manufactured by TA Instruments, Inc., AR-G2)was preheated to 30° C. and kept as it was until the temperature becamestable. After the temperature was found to be stable, the epoxy resincomposition was isolated into a plate, the gap was adjusted, and thenthe measurement was started under the following condition. For 10minutes, 10 spots were measured, and the average thereof was adopted asviscosity.

Measurement mode: constant stress,

Level of stress: 300 Pa,

Frequency: 1.59 Hz,

Plate diameter: 25 mm,

Plate type: parallel plate,

Plate gap: 0.5 mm.

(Measurement of Viscosity Under Heating Condition)

Immediately after being prepared, the epoxy resin composition was putand sealed into an airtightable container, and stored by being left tostand in a room at 23° C. in a place protected from direct sunlight.Seven days after the preparation of the epoxy resin composition, theviscosity of the composition was measured as below.

The plate of a rheometer (manufactured by Thermo Fisher Scientific,MARS40) was preheated to 30° C. and kept as it was until the temperaturebecame stable. After the temperature was found to be stable, the epoxyresin composition was isolated into a plate, the gap was adjusted, andthen the measurement was started under the following condition. For 10minutes, 10 spots were measured, and the average thereof was adopted asviscosity.

Measurement mode: constant stress,

Level of stress: 300 Pa,

Frequency: 1.59 Hz,

Plate diameter: 25 mm,

Plate type: parallel plate,

Plate gap: 0.5 mm

Temperature: increased at 2° C./min from 30° C. to a temperature atwhich the curing reaction of the epoxy resin composition was about tostart (that is, a temperature at which the viscosity was rapidlyincreased)

(Evaluation of Viscosity)

The viscosity of the epoxy resin composition measured at 30° C. 30minutes after the preparation of the composition is a measure ofimpregnation properties at the time of impregnating reinforcing fiberwith the epoxy resin composition. The viscosity after 30 minutes wasevaluated based on the following standards.

A: the viscosity after 30 minutes was equal to or lower than 15 Pa·s(impregnation properties were excellent).

B: the viscosity after 30 minutes was higher than 15 Pa·s.

The viscosity of the epoxy resin composition measured at 30° C. 10 daysafter the preparation of the composition is a measure for determiningwhether SMC demonstrates appropriate tackiness and draping propertieswithin a short period of time and whether excellent handleability ismaintained. The viscosity after 10 days was evaluated based on thefollowing standards.

A: the viscosity after 10 days was 2,000 to 55,000 Pa·s (handleabilitywas excellent).

B: the viscosity after 10 days is less than 2,000 Pa·s or higher than55,000 Pa·s.

The viscosity of the epoxy resin composition measured at 30° C. 20 daysafter the preparation of the composition is a measure for determiningwhether a thickened material in a B stage is obtained which enables SMCto demonstrate appropriate tackiness or draping properties. Furthermore,the viscosity of the epoxy resin composition measured at 30° C. 20 daysafter the preparation of the composition is a measure for determiningwhether the B stage is maintained for a long period of time (B stagestability). The viscosity after 20 days was evaluated based on thefollowing standards.

A: the viscosity after 20 days was 2,000 to 50,000 Pa·s (B stagestability was excellent).

B: the viscosity after 20 days was less than 2,000 Pa·s or higher than100,000 Pa·s.

(Rate of Change in Viscosity (c) and Viscosity (b))

The value of [viscosity (c)]/[viscosity (b)] is a measure of storagestability of SMC.

The value of [viscosity (c)]/[viscosity (b)] was evaluated based on thefollowing standards.

A: the value of [viscosity (c)]/[viscosity (b)] was equal to or smallerthan 3 (storage stability was excellent).

B: the value of [viscosity (c)]/[viscosity (b)] was greater than 3.

(Evaluation of Viscosity Under Heating Condition)

The viscometry under heating condition is a measure of fluidity of SMCat the time of press molding. Regarding the result of the viscometryunder a heating condition, the higher the viscosity at which the curingreaction of the epoxy resin composition is about to start (that is, thehigher the viscosity that will be rapidly increased), the further theoccurrence of burrs at the time of press molding can be inhibited. Theviscosity under a heating condition was evaluated based on the followingstandards.

A: the viscosity after 7 days at which the curing reaction of the epoxyresin composition was about to start is 0.5 Pa·s to 500 Pa·s (fluidityof SMC at the time of press molding was excellent).

B: the viscosity after 7 days at which the curing reaction of the epoxyresin composition was about to start was less than 0.5 Pa·s or higherthan 500 Pa·s.

(Evaluation of Occurrence of Burrs)

In a case where the number of burrs occurring in a molding die is small,the burrs can be removed within a short period of time after molding.Accordingly, the molding cycle can be shortened.

A die having a size of 300 mm (length)×300 mm (width)×2 mm (thickness)was charged with a laminated substance obtained by laminating SMC havinga size of 300 mm (length)×300 mm (width) in 2 ply. Under the conditionof a die temperature of 140° C. and a pressure of 4 MPa, the laminatedsubstance was heated and compressed for 5 minutes, thereby obtaining a300 mm×300 mm flat plate-like fiber-reinforced composite material havinga thickness of about 2 mm (CFRP molding plate). A burr occurrence rateat the time of manufacturing the CFRP molding plate was calculated bythe following equation.

(X−Y)/(X)×100

Herein, X represents the weight of SMC with which the die was charged,and Y represents the weight of the molded article taken out of the dieafter molding.

The standards for evaluating the occurrence of burrs are as below.

A (excellent): the burr occurrence rate calculated by the above equationwas less than 10%.

B (defective): the burr occurrence rate calculated by the above equationwas equal to or higher than 10%.

(Quick Curing Properties)

The epoxy resin composition was weighed and put into a standard Hermeticaluminum pan of a differential scanning calorimeter (manufactured by TAInstrument, Inc., Q1000), and a standard aluminum lid of the device wasput on the pan, thereby creating a sample According to the temperaturecontrol program of the device, the sample was heated to 140° C. from 30°C. at 200° C./min and then kept under an isothermal condition at 140° C.for 30 minutes. In this way, a DSC heating curve of the epoxy resincomposition at a series of control temperatures was obtained. In the DSCheating curve, a tangent was drawn from a point, at which the slope of acurve is maximum along which the heating amount was getting reduced fromthe peak of the heating amount, and a tangent (baseline) was drawn froma portion where the heating resulting from the curing reaction wasstopped. The time on the intersection point between these tangents wasadopted as a curing finish time. The curing finish time is a measure ofa molding time of a molding material. The quick curing properties wereevaluated based on the following standards.

A: the curing finish time was equal to or shorter than 10 minutes (quickcuring properties were excellent).

B: the curing finish time was longer than 10 minutes.

(Preparation of Cured Resin Plate)

The epoxy resin composition was defoamed in a vacuum and injected intothe space between two sheets of glass plates having a thickness of 4 mmbetween which a polytetrafluoroethylene spacer having a thickness of 2mm was interposed. Under the condition by which the surface temperatureof the glass plates became 140° C., the epoxy resin composition washeated for 10 minutes in a hot air circulation-type thermostatic furnaceand then cooled, thereby obtaining a cured resin plate.

(Bending Characteristics)

Six sheets of test pieces having a width of 8 mm and a length of 60 mmwere cut out of the cured resin plate. By using an all-purpose tester(manufactured by Instron, INSTRON 4465), bending strength, flexuralmodulus, bending elongation at break, and bending elongation at yieldwere measured under the following condition, and the average of the 6sheets was determined.

Crosshead speed; 2 mm/min,

Span length: set by actually measuring the thickness of the cured resinplate and multiplying the thickness by 16 (unit mm)

(Heat Resistance)

The cured resin plate was processed into a 55 mm (length)×12.5 mm(width) test piece and measured at a measurement frequency of 1 Hz and aheating rate of 5° C./min by using a rheometer (TA Instrument, Inc.,ARES-RDA). log G′ was plotted for temperature, and a temperature on anintersection point between an approximating line of a region where logG′ was constant and an approximating line of a region where log G's wasrapidly reduced was recorded as a glass transition temperature (G′−Tg (°C.)). The peak top of Log G″ was denoted as G″−Tg (° C.). The peak topof tan δ was denoted as tan δ (° C.). The heat resistance was evaluatedbased on the following standards.

A: the glass transition temperature (G′−Tg) was equal to or higher than130° C. (heat resistance was excellent).

B: the glass transition temperature (G′−Tg) was less than 130° C.

TABLE 1 Example 1 2 3 4 5 6 Component jER ®828 100 100 100 100 100 100(A) Component HN-2200 14 14 12.5 12.5 11 11 (B) Component 2MZA-PW 4 6 46 4 6 (C) Epoxy group equivalent 0.54 0.54 0.54 0.54 0.54 0.54 Acidanhydride group equivalent 0.17 0.17 0.15 0.15 0.13 0.13 Acid anhydridegroup/epoxy 0.31 0.31 0.28 0.28 0.25 0.25 group Viscosity at After 30minutes 2.6 2.7 2.8 2.9 2.9 3.2 30° C. (Pa · s) After 10 days 436 1545534 1,518 651 1,159 (Pa · s) After 20 days 11,260 9,463 4,571 5,3842,198 3,093 (Pa · s) Evaluation of A A A A A A viscosity after 30minutes Evaluation of A A A A A A viscosity after 20 days Quick curingCuring finish time 6 5 6 6 7 6 properties (min) Evaluation of A A A A AA quick curing properties Bending Bending strength 139.9 143.5 139.8133.8 143.1 134.1 characteristics (MPa) Flexural modulus 3.44 3.46 3.453.45 3.4 3.4 (GPa) Bending 5.25 5.71 5.11 5.15 5.64 5.54 elongation atbreak (%) Bending 5.24 5.7 5.1 5.15 5.63 5.53 elongation at yield (%)Heat G′-Tg(° C.) 137 144 137 142 138 148 resistance G″-Tg (° C.) 147 154147 153 148 159 tan δ (° C.) 165 171 166 173 168 177 Evaluation of heatA A A A A A resistance

TABLE 2 Example 7 8 9 10 11 12 Component jER ®828 100 80 5 100 100 100(A) jER ®807 95 jER ®630 20 Component HN-2200 14 14 14 10 14 14 (B)Component 2MZA-PW 5 5 5 5 5 5 (C) Component DTCYANEX1400F 1 0.5 (D)Component 2E4MZ 0.03 0.03 0.03 0.05 (E) Epoxy group equivalent 0.54 0.640.6 0.54 0.54 0.54 Acid anhydride group equivalent 0.17 0.17 0.17 0.120.17 0.17 Acid anhydride group/epoxy group 0.31 0.26 0.28 0.22 0.31 0.31Viscosity at After 30 minutes 3 2 1 5 3 3 30° C. (Pa · s) After 10 days6,207 4,592 1,027 2,403 8,706 7,902 (Pa · s) After 20 days 12,290 6,9212,204 6,017 16,880 12,500 (Pa · s) Evaluation of A A A A A A viscosityafter 30 minutes Evaluation of A A A A A A viscosity after 20 days Quickcuring Curing finish time 6 5 5 5 6 6 properties (min) Evaluation of A AA A A A quick curing properties Bending Bending strength 145.8 144.6155.1 134.7 147.2 139.7 characteristics (MPa) Flexural modulus 3.34 3.533.56 3.49 3.31 3.32 (GPa) Bending 6.27 5.68 6.62 5.1 8.86 6.56elongation at break (%) Bending 6.26 5.67 6.6 5.09 7.64 6.38 elongationat yield (%) Heat G′-Tg(° C.) 144 149 136 143 152 152 resistance G″-Tg(° C.) 154 161 143 155 160 160 tan δ (° C.) 170 182 155 174 173 174Evaluation of heat A A A A A A resistance

TABLE 3 Example 13 14 15 16 17 Component jER ®828 100 100 100 100 100(A) Component HN-2200 14 (B) HN-2000 14 14 HN-5500 14.2 14.2 Component2MZA-PW 6 6 5 5 5 (C) Component 2E4MZ 0.07 0.07 0.07 (E) Epoxy groupequivalent 0.54 0.54 0.54 0.54 0.54 Acid anhydride group equivalent 0.170.17 0.17 0.17 0.17 Acid anhydride group/epoxy group 0.31 0.31 0.31 0.310.31 Viscosity at After 30 minutes 3 4 4 3 4 30° C. (Pa · s) After 10days 1,853 1,680 7,793 10,200 4,386 (Pa · s) After 20 days 15,860 33,21016,040 41,780 32,870 (Pa · s) Evaluation of A A A A A viscosity after 30minutes Evaluation of A A A A A viscosity after 20 days Quick curingCuring finish time 6 6 5 5 5 properties (min) Evaluation of quick A A AA A curing properties Bending Bending strength 138.7 135 137.5 141.3144.6 characteristics (MPa) Flexural modulus 3.4 3.44 3.47 3.54 3.56(GPa) Bending elongation 5.39 4.93 5.53 5.56 5.67 at break (%) Bendingelongation 5.38 4.92 5.53 5.55 5.66 at yield (%) Heat G′-Tg(° C.) 141139 140 134 134 resistance G″-Tg (° C.) 151 149 149 144 144 tan δ (° C.)168 168 167 163 162 Evaluation of heat A A A A A resistance

TABLE 4 Example 18 19 20 21 22 23 Component jER ®828 95 95 95 95 95 95(A) TETRAD-X 5 5 5 5 5 5 Component HN-2200 12.5 12.5 12.5 13.8 13.8 13.8(B) Component 2MZA-PW 6 6 4 5 5 5 (C) Other Omicure ®24 2 componentsComponent DICYANEX1400F 2 2 4 2 (D) Epoxy group equivalent 0.56 0.560.56 0.56 0.56 0.56 Acid anhydride group equivalent 0.15 0.15 0.15 0.170.17 0.17 Acid anhydride group/epoxy group 0.27 0.27 0.27 0.3 0.3 0.3Viscosity at After 30 minutes 4 4 4 3 4 4 30° C. (Pa · s) After 10 days3,725 3,454 2,919 8,683 7,172 11,170 (Pa · s) After 20 days 3,802 5,6663,415 10,380 13,830 16,250 (Pa · s) Evaluation of A A A A A A viscosityafter 30 minutes Evaluation of A A A A A A viscosity after 20 days Quickcuring Curing finish time 5 6 5 7 9 7 properties (min) Evaluation of A AA A A A quick curing properties Bending Bending strength 130.1 150.1135.7 148.3 162 124.5 characteristics (MPa) Flexural modulus 3.38 3.293.41 3.33 3.49 3.37 (GPa) Bending 5.13 9.46 5.32 9.7 10.69 4.41elongation at break (%) Bending 5.12 7.56 5.32 7.69 7.6 4.41 elongationat yield (%) Heat G′-Tg(° C.) 144 154 137 154 148 149 resistance G″-Tg(° C.) 158 162 150 162 155 155 tan δ (° C.) 175 172 167 171 163 163Evaluation of heat A A A A A A resistance

TABLE 5 Comparative Example 1 2 3 Component (A) jER ®828 jER ®807 70 7070 jER ®604 30 30 30 Component (B) HN-2200 MHAC-P 10 15 20 Component (C)2MZA-PW Component (D) 2E4MZ Other components DY9577 5 2 5 Epoxy groupequivalent 0.42 0.42 0.42 Acid anhydride group equivalent 0.1 0.15 0.2Acid anhydride group/epoxy group 0.23 0.35 0.47 Viscosity at 30° C.After 30 minutes 3 2 1 (Pa · s) After 10 days 22 49 58 (Pa · s) After 20days 101 946 2,568 (Pa · s) Evaluation of A A A viscosity after 30minutes Evaluation of B B A viscosity after 20 days Quick curing Curingfinish 14 11 12 properties time (min) Evaluation of B B B quick curingproperties

The epoxy resin compositions of Examples 1 to 23 have a low viscosity 30minutes after the preparation of the compositions and exhibit excellentimpregnation properties at the time of manufacturing SMC. Furthermore,10 days after the preparation of these epoxy resin compositions, thesecompositions have appropriately shifted to the B stage. In a case wherethese compositions are made into SMC, the tackiness and drapingproperties thereof are appropriate. In addition, the B stage stabilitythereof is also excellent. These compositions also have excellent quickcuring properties, and in a case where the compositions are made intoSMC, they can be molded within a short period of time. The curedmaterial of SMC obtained from the epoxy resin compositions of Examples 1to 23 less causes burrs, and the bending strength, flexural modulus, andheat resistance thereof are also high.

Comparative Examples 1 and 2 are examples in which epoxy resincompositions are prepared with reference to PTL 6 to 8. The epoxy resincompositions of Comparative Examples 1 and 2 have a low viscosity 30minutes after the preparation of the compositions and exhibit excellentimpregnation properties. However, these compositions have a lowviscosity 20 days after the preparation of the compositions and haveextremely strong tackiness. In a case where these compositions are usedas a molding material, due to the strong tackiness, the handleabilitythereof is poor. Furthermore, because the quick curing propertiesthereof are poor, it takes a long time to cure the compositions. In acase where these compositions are used as a molding material, the timefor which the material stays in a die is lengthened.

Comparative Example 3 is an example in which an epoxy resin compositionis prepared with reference to PTL 6 to 8. The epoxy resin compositionsof Comparative Example 3 has a low viscosity 30 minutes after thepreparation of the composition and exhibits excellent impregnationproperties. Furthermore, 20 days after the preparation of thecomposition, the composition has appropriately shifted to the B stage.In a case where the composition is used as a molding material, thetackiness and draping properties thereof are appropriate. However,because the quick curing properties thereof are poor, it takes a longtime to cure the composition. In a case where the composition is used asa molding material, the time for which the material stays in a die islengthened.

Manufacturing of Fiber-Reinforced Composite Material Examples 24 to 26

By using a doctor blade, a carrier film made of polyethylene was coatedwith the epoxy resin composition formulated as shown in Table 6 at 600g/m². On the epoxy resin composition, chopped carbon fiber tows, whichwere obtained by cutting a carbon fiber tow constituted with 15,000filaments (manufactured by Mitsubishi Rayon Co., Ltd., TR50S 15L) in alength of 25 mm, were scattered such that the basis weight of the carbonfiber substantially became uniform at 1,200 g/m² and the fiber directionof the carbon fiber became random.

By using a doctor blade, a carrier film made of polyethylene was coatedwith the same epoxy resin composition at 600 g/m².

The chopped carbon fiber tows were sandwiched between two sheets of thecarrier films such that the side of the epoxy resin composition becameinside. The carrier films were pressed by being passed between rollssuch that the chopped carbon fiber tows were impregnated with the epoxyresin composition, thereby obtaining a SMC precursor.

The SMC precursor was left to stand at room temperature (23° C.) for 20days such that the epoxy resin composition in the SMC precursor wassufficiently thickened, thereby obtaining SMC.

SMC was laminated in 2ply, a molding die was charged with the laminatedSMC at a charge ratio of 65% (ratio of the area of SMC to the area ofthe die), and SMC was heated and compressed for 5 minutes under thecondition of a die temperature of 140° C. and a pressure of 4 MPa suchthat the epoxy resin composition was cured, thereby obtaining a 200mm×300 mm flat plate-like fiber-reinforced composite material having athickness of about 2 mm (CFRP molding plate). The following measurementand evaluation were performed. The results are shown in Table 6.

(Impregnation Properties)

The SMC precursor was cut in a length of about 30 cm, and theimpregnation condition was visually checked and evaluated based on thefollowing standards.

A: dry carbon fiber and the like were not on the cut surface, and theimpregnation properties were excellent.

B: dry carbon fiber was checked on the cut surface, and the impregnationproperties were not excellent.

(Tackiness)

The tackiness of SMC was evaluated based on the following standards.

A: SMC felt appropriately tacky to the touch, and SMC could be laminatedin a simple manner.

B: SMC felt very tacky to the touch, or it was difficult to laminate SMCbecause the tackiness thereof was weak.

(Draping Properties)

The draping properties of SMC were evaluated based on the followingstandards.

A: SMC was appropriately flexible to the touch, and it was easy to cutand carry SMC.

B: SMC was poorly flexible to the touch, and it was difficult to cut andcarry SMC.

(Handleability)

The handleability of SMC was evaluated based on the following standards.

A: both the tackiness and draping properties were evaluated as A.

B: either or both of the tackiness and draping properties were evaluatedas B.

(Heat Resistance)

The CFRP molding plate was processed into a 55 mm (length)×12.5 mm(width) test piece and measured at a measurement frequency of 1 Hz and aheating rate of 5° C./min by using a rheometer (TA Instrument, Inc.,ARES-RDA). log G′ was plotted for temperature, and a temperature on anintersection point between an approximating line of a region where logG′ was constant and an approximating line of a region where log G's wasrapidly reduced was recorded as a glass transition temperature (G′−Tg (°C.)). The peak top of Log G″ was denoted as G″−Tg (° C.). The peak topof tan δ was denoted as tan δ (° C.). The heat resistance was evaluatedbased on the following standards.

A: the glass transition temperature (G′−Tg) was equal to or higher than130° C. (heat resistance was excellent).

B: the glass transition temperature (G′−Tg) was less than 130° C.

TABLE 6 Example 24 25 26 Component (A) jER ®828 100 90 90 TETRAD-X 10 10Component (B) HN-2200 11 12.4 12.4 Component (C) 2MZA-PW 6 6 6 Component(D) DICYANEX1400F 6 1 Epoxy group equivalent 0.54 0.58 0.58 Acidanhydride group equivalent 0.13 0.15 0.15 Acid anhydride group/epoxygroup 0.25 0.26 0.26 Impregnation properties A A A Tackiness A A ADraping properties A A A Handleability A A A Heat resistance G′-Tg(° C.)140 163 153 G″-Tg (° C.) 150 130 167 tan δ (° C.) 166 170 173 Evaluationof A A A heat resistance

By using the epoxy resin compositions of Examples 24 to 26, SMC wasprepared, and fiber-reinforced composite materials were manufactured.The impregnation properties, tackiness, and draping properties thereofwere excellent, and the handleability thereof was extremely excellent.Furthermore, the heat resistance thereof was high, and at the time oftaking the fiber-reinforced composite material out of a die, thematerial maintained sufficient stiffness and exhibited excellent moldrelease properties as well.

Preparation of Epoxy Resin Composition Examples 27 to 30

According to the formulation shown in Table 7, epoxy resin compositionswere obtained in the same manner as in Examples 1 to 23. The epoxy resincompositions were measured and evaluated in the same manner as inExamples 1 to 23. The results are shown in Table 7.

TABLE 7 Example Example Example Example 27 28 29 30 Component jER ®82895 95 95 95 (A) TETRAD-X 5 5 5 5 Component HN-2200 12 10 5 (B) MH-700TMEG-600 2 4.5 MTA-15 12 8 Component 2MZA-PW 5 5 5 5 (C) ComponentDICY1400F 1 1 1 1 (D) Epoxy group equivalent [g/eq.] 0.56 0.56 0.56 0.56Acid anhydride group equivalent [g/eq.] 0.07 0.15 0.14 0.11 Acidanhydride group/epoxy group 0.13 0.28 0.25 0.19 Viscosity at Viscometry(a) after 30 11 4 6 6 30° C. minutes (Pa · s) Viscometry (b) after 10days 15,790 11,030 8,559 11,140 (Pa · s) Viscometry (c) after 20 days11,060 12,040 10,740 11,410 (Pa · s) (c)/(b) 0.7 1.1 1.3 1.0 Evaluationof viscosity after A A A A 30 minutes Evaluation of viscosity after A AA A 20 days Evaluation of viscosity after A A A A 20 days ViscosityMinimum viscosity [Pa · s] 1.1 0.7 1.1 1.1 under heating Temperature atminimum 123 117 120 117 condition viscosity [° C.] Fluidity A A A AOccurrence of Burr occurrence rate [%] 4 8 6 6 burr Evaluation ofoccurrence of A A A A burr Quick curing Curing finish time (min) 7.0 6.56.8 6.6 properties Evaluation of quick curing A A A A properties BendingBending strength (MPa) 151 142 132 158 characteristics Flexural modulus(GPa) 3.40 3.41 3.47 3.46 Bending elongation at break 6.84 5.47 4.538.33 (%) Bending elongation at yield 6.77 5.47 4.53 7.69 (%) HeatG′-Tg(° C.) 156 157 156 158 resistance G″-Tg (° C.) 168 166 165 166 tanδ (° C.) 185 180 181 181 Evaluation of heat resistance A A A A

The epoxy compositions of Examples 27 to 30 have a low viscosity 30minutes after the preparation of the compositions, and at the time ofmanufacturing SMC, the compositions exhibit excellent impregnationproperties. Furthermore, 10 days after the preparation of these epoxyresin compositions, these compositions have appropriately shifted to theB stage. In a case where these compositions are made into SMC, thetackiness and draping properties thereof are appropriate. In addition,the B stage stability thereof is also excellent. These compositions alsohave excellent quick curing properties, and in a case where thecompositions are made into SMC, they can be molded within a short periodof time. The cured material of SMC obtained from the epoxy resincompositions of Examples 27 to 30 less causes burrs, and the bendingstrength, flexural modulus, and heat resistance thereof are also high.

INDUSTRIAL APPLICABILITY

The sheet molding compound of the present invention is excellent in thereinforcing fiber impregnation properties, the tackiness and drapingproperties after the shift to the B stage, the B stage stability(fluidity at the time of press molding), the quick curing properties atthe time of heating (staying in a die for a short period of time at thetime of press molding), and forms a cured material having excellent heatresistance. Furthermore, owing to its excellent mechanicalcharacteristics and heat resistance after curing, the sheet moldingcompound of the present invention is suitable as a raw material ofstructural parts for industries and automobiles.

1. A sheet molding compound which is a thickened material of an epoxyresin composition, comprising: a component (A); a component (B); and acomponent (C), wherein the component (A) is an epoxy resin staying in aliquid state at 25° C., the component (B) is an acid anhydride, thecomponent (C) is an epoxy resin curing agent, and in the thickenedmaterial, at least some of epoxy groups of the component (A) and atleast some of carboxy groups derived from the component (B) form ester.2. The sheet molding compound according to claim 1, further comprising:reinforcing fiber.
 3. The sheet molding compound according to claim 1,wherein a viscosity of the epoxy resin composition that is measured byviscometry (a) at 30° C. 30 minutes after the preparation of thecomposition described below is 0.5 to 15 Pa·s, viscometry (a):immediately after being prepared, the epoxy resin composition is put andsealed into an airtightable container and left to stand for 30 minutesat 23° C., and then a viscosity of the epoxy resin composition at 30° C.is measured.
 4. The sheet molding compound according to claim 1, whereina viscosity of the epoxy resin composition that is measured byviscometry (b) at 30° C. 10 days after the preparation of thecomposition described below is 2,000 to 55,000 Pa·s, viscometry (b):immediately after being prepared, the epoxy resin composition is put andsealed into an airtightable container and left to stand for 10 days at23° C., and then a viscosity of the epoxy resin composition at 30° C. ismeasured.
 5. The sheet molding compound according to claim 1, wherein aviscosity of the epoxy resin composition that is measured by viscometry(c) at 30° C. 20 days after the preparation of the composition describedbelow is 2,000 to 100,000 Pa·s, viscometry (c): immediately after beingprepared, the epoxy resin composition is put and sealed into anairtightable container and left to stand for 20 days at 23° C., and thena viscosity of the epoxy resin composition at 30° C. is measured.
 6. Thesheet molding compound according to claim 1, wherein a viscosity of theepoxy resin composition that is measured by viscometry (b) at 30° C. 10days after the preparation of the composition by is 2,000 to 55,000Pa·s, the viscosity of the epoxy resin composition that is measured byviscometry (c) at 30° C. 20 days after the preparation of thecomposition described below is 2,000 to 100,000 Pa·s, and a viscosity(b) measured by the viscometry (b) and a viscosity (c) measured by theviscometry (c) satisfy a relationship of [viscosity (c)]/[viscosity(b)]≤3, viscometry (b): immediately after being prepared, the epoxyresin composition is put and sealed into an airtightable container andleft to stand for 10 days at 23° C., and then a viscosity of the epoxyresin composition at 30° C. is measured, viscometry (c): immediatelyafter being prepared, the epoxy resin composition is put and sealed intoan airtightable container and left to stand for 20 days at 23° C., andthen a viscosity of the epoxy resin composition at 30° C. is measured.7. The sheet molding compound according to claim 1, wherein a content ofthe component (B) is such that the amount of acid anhydride groups withrespect to 1 equivalent of epoxy groups contained in the epoxy resincomposition becomes 0.1 to 0.5 equivalents.
 8. The sheet moldingcompound according to claim 1, wherein a content of the component (B) is3 to 30 parts by mass with respect to 100 parts by mass of the entireepoxy resin contained in the epoxy resin composition.
 9. The sheetmolding compound according to claim 1, wherein a content of thecomponent (C) is 0.1 to 25 parts by mass with respect to 100 parts bymass of the entire epoxy resin contained in the epoxy resin composition.10. The sheet molding compound according to claim 1, wherein thecomponent (A) contains a glycidyl amine-based epoxy resin.
 11. The sheetmolding compound according to claim 10, wherein a content of theglycidyl amine-based epoxy resin with respect to 100 parts by mass ofthe entire epoxy resin contained in the epoxy resin composition is 1 to30 parts by mass.
 12. The sheet molding compound according to claim 1,wherein the component (B) stays at a liquid state at 25° C.
 13. Thesheet molding compound according to claim 1, wherein the component (C)stays at a solid state at 25° C.
 14. The sheet molding compoundaccording to claim 1, wherein the component (B) contains a compoundhaving two cyclic acid anhydrides in a molecule.
 15. The sheet moldingcompound according to claim 1, wherein the component (B) contains aphthalic anhydride or a hydrogenated phthalic anhydride that may have asubstituent.
 16. The sheet molding compound according to claim 1,wherein the component (B) contains a hydrogenated phthalic anhydridethat may have a substituent, and the hydrogenated phthalic anhydridethat may have a substituent is a compound represented by Formula (1) ora compound represented by Formula (2).


17. The sheet molding compound according to claim 1, wherein thecomponent (C) contains an imidazole-based compound having a meltingpoint of 120° C. to 300° C.
 18. The sheet molding compound according toclaim 1, wherein the epoxy resin composition further contains acomponent (D), the component (1)) is dicyandiamide, and a content of thecomponent (D) with respect to 100 parts by mass of the entire epoxyresin contained in the epoxy resin composition is 0.1 to 5 parts bymass.
 19. The sheet molding compound according to claim 1, wherein thecomponent (C) further contains a component (E), the component (E) is animidazole-based compound staying in a liquid state at 25° C., and acontent of the component (E) with respect to 100 parts by mass of theentire epoxy resin contained in the epoxy resin composition is 0.01 to0.2 parts by mass.
 20. A fiber-reinforced composite material which is acured material of the sheet molding compound according to claim 1.